Meeting Abstract
Rayleigh–Bénard convection cells, which are widespread in nature, are flow instabilities driven by a thermal gradient between a heated surface and its surroundings. For flying insects that live in urban environments, these perturbed flows represent a challenge because artificial surfaces exposed to solar radiation can reach extreme temperatures (up to 100 ºC), generating significant unsteady flows. We examined the effect of thermal convection cells on fruit flies (Drosophila melanogaster), which inhabit urban environments and fly close to surfaces on which convection cells may form. We performed repeated measurements on individual flies (n=32) to compare their performance when flying across a chamber (22 × 12 × 8 cm) through still air and through turbulent convection cells (Ra~107 and Pr~0.7). In general, flight performance declined when flies were exposed to turbulent convection conditions: 34 % of individuals experienced flight control losses and fell to the ground, and 50% reached their target but displayed lower average speeds than during control flights. While some wing kinematics were affected at the end of the trial in these individuals, average pitch angle was steeper in the presence of turbulent convection, and mass-specific mechanical energy was lower. In contrast, the remaining 16% of individuals displayed improved flight performance (higher speed, acceleration, and kinetic energy) during perturbed conditions, and their trajectories show that they took advantage of the flows generated by convection. Our results suggest that although turbulent convection represents a serious control challenge for insect fliers, it can be advantageous if insects choose a trajectory that allows them to effectively extract energy from these environmental flows.
